1. Field of the Invention
This invention relates to a method and apparatus for separating color and luminance signals from a composite video signal, and more specifically to a method and apparatus for separating color and luminance signals in consideration of the existence and degree of a motion.
2. Background of the Related Art
Typically, the video signal modulation method of a color television is classified into an NTSC (National Television System Committee), PAL (Phase Alternation by Line), SECAN (Sequential Couleur a Memoire) in accordance with the is method of modulating the color and the luminance signal.
In the NTSC standard, a subcarrier is modulated and a color signal C comprising I and Q components is frequency-interleaved into a luminance signal Y so as to use effectively frequency bandwidths.
Then, the encoded composite video signal is received through a color television receiver, separated into the color and the luminance signal, and then displayed on a monitor. At this time, the bandwidth of the color signal is 3.58 MHz and that of the luminance signal is 4 MHz.
However, if the composite video signal is incompletely separated into the color and the luminance signal, the picture quality is distorted or undesirable patterns are displayed due to cross luminance or cross color.
Therefore, color/luminance separation circuits have been provided to solve the problem.
As shown in FIG. 1, a conventional color/luminance separation circuit comprises a composite video signal output section 1 for receiving and outputting a composite video signal, and a composite signal separator 2 for separating the inputted composite video signal into the color and the luminance signal.
The composite signal separator 2 uses a line comb filter to filter spatially the composite video signal, separate into the color and luminance signal, and output the separated signals.
Hereinafter, the configuration and operation of the composite signal separator will be described in detail with reference to FIG. 2.
The composite signal separator 2 comprises a delay section 3, a first subtractor 4, an amplifier 5, a band pass filter 6, and a second subtractor 7.
First, the composite video signal being inputted through an antenna is transmitted to the delay section 3 to delay for the duration of 1 horizontal scan line 1H.
Then, the first subtractor 4 subtracts the outputted signal from the delay section 3 from the current composite video signal and outputs the resulting signal. The resulting signal represents the color signal C which is subtracted from the component of the luminance signal Y from the composite video signal.
Then, the resulting color signal is amplified in the amplifier 5, and the amplified color signal is filtered to 3.59 MHz in the band pass filter 6. As a result, the color signal C is filtered from the composite video signal. Meanwhile, the second subtractor 7 subtracts the color signal C with 3.58 MHz bandwidth from the current composite video signal. As a result, a luminance signal Y is filtered from the composite video.
Thus, the composite signal separator 2 performs the phase inversion of the two horizontal scan lines in the composite video signal to provide the separated color signal and the separated luminance signal.
However, the above-described conventional color/luminance signal separation circuit has problems and produces a hanging dot or a sitting dot when a motion exists on the video image. Because of adding the color signal to the luminance signal, the hanging dot is produced when the color and the luminance signal are separated from the composite video signal.
To solve the above-described problems, another color/luminance signal separation circuit with respect to the image motion has been developed.
As shown in FIG. 3, the separation circuit includes a composite signal output section 10, first and second filters 20, 30, an image motion detector 40 for outputting a control signal when the image motion is detected, a color signal selector 50 for selecting one of the first and second color signals according to the control signal, and a luminance signal selector 60 for selecting one of the first and second luminance signals according to the control signal.
The first filter 20 uses the frame comb filter which filters temporally the composite video signal, and the second filter 30 uses the line comb filter which filters spatially the composite video signal,
Therefore, the above-described color/luminance signal separation circuit outputs the first color and luminance signals C1, Y1, being separated by the first filter 20, and the second color and luminance signals C2, Y2, being separated by the second filter 30.
The first filter 20 performs the processing of phase inversion of the color signals in the frames to separate the first color signal C1 and the first luminance signal Y1. However, the second filter 30 performs the processing of phase inversion of the color signals in the horizontal scan lines to separate the second color signal C2 and the second luminance signal Y2.
The motion detector 40 receiving the composite video signal from the output section 10 detects existence of the motion in the composite video signal using the temporal frame difference of the composite video signal. The temporal frame difference is obtained from the difference between the current and previous frames.
If the temporal frame difference is zero, the motion detector 40 outputs the control signal with “0” level to the color and the luminance signal selector 50, 60, respectively. And if not, the motion detector 40 outputs the control signal with “1” level to the selectors 50, 60, respectively.
Then, if the control signal from the motion detector 40 is zero, the selectors 50, 60 output the first color signal C1 and the first luminance signal Y1 in accordance with the control signal, respectively. And if not, the selectors 50, 60 output the second color signal C2 and the second luminance signal Y2, respectively.
Accordingly, the conventional separation circuit detects the existence of the motion from the composite video signal, and then selects and outputs the color and the luminance signals in accordance with the existence of the image motion.
However, the above-described conventional separation circuit has the following problems.
First, as the circuit does not detect the degree of the motion, it can not separate completely the color and the luminance signals from the composite video signal.
Second, although the conventional separation circuit separates the color and the luminance signals after determining the existence of the motion, it an not be protected from cross color or the cross luminance effects, as it uses the conventional line comb filter.